Report: More vitamin D is good, but easy does it

by Lauran Neergaard - Nov. 30, 2010 12:00 AMAssociated Press

WASHINGTON - Got milk? You may need a couple of cups more than today's food labels say to get enough vitamin D for strong bones. But don't go overboard: Long-awaited new dietary guidelines say there's no proof that megadoses prevent cancer or other ailments - which is sure to frustrate backers of the so-called sunshine vitamin.

The decision by the prestigious Institute of Medicine, the health arm of the National Academy of Sciences, could put some brakes on the nation's vitamin D craze, warning that superhigh levels could be risky.

"More is not necessarily better," cautioned Dr. Joann Manson of Harvard Medical School, who co-authored the Institute of Medicine's report being released today.

Most people in the U.S. and Canada, from age 1 to 70, need to consume no more than 600 international units of vitamin D a day to maintain health, the report found. People in their 70s and older need as much as 800 IUs. The report set those levels as the "recommended dietary allowance" for vitamin D.

That's a bit higher than the target of 400 IUs set by today's government-mandated food labels and higher than 1997 recommendations by the Institute of Medicine that ranged from 200 to 600 IUs, depending on age.

But it's far below the 2,000 IUs a day that some scientists recommend, pointing to studies that suggest people with low levels of vitamin D are at increased risk of certain cancers or heart disease.

"Have they gone far enough? In my opinion probably not, but it's a step in the right direction," said Dr. Michael Holick of Boston University Medical Center, a prominent vitamin D researcher who said the new levels draw needed attention to the vitamin D debate.

But the two-year study by the Institute of Medicine's panel of experts concluded that research into vitamin's D possible roles in other diseases is conflicting. Some studies show no effect, or even signs of harm.

A National Cancer Institute study last summer was the latest to report no cancer protection from vitamin D and the possibility of an increased risk of pancreatic cancer in people with the very highest D levels. Superhigh doses (above 10,000 IUs a day) are known to cause kidney damage, and the report sets 4,000 IUs as an upper daily limit - but not the amount people should strive for.

But here's the report's big surprise: Although some people truly are seriously deficient in vitamin D, the average American in fact already has enough circulating in the blood - because we also make vitamin D from sun exposure and because many people already take multivitamins or other D-containing dietary supplements.